This invention relates to electromechanical valve control circuitry in general and particularly to driving circuitry for controlling single-coil fuel injectors. More particularly, this invention relates to a driver circuit and method for driving single-coil fuel injectors with a two-pin input connector.
Minimizing heat generation is important for fuel injectors that inject high vapor pressure fuels such as, for example, Liquid Propane Gas (LPG). Excessive heat generation within LPG fuel injectors often results in vapor lock because LPG is highly volatile and can boil at relatively low temperatures. Vapor lock is an undesirable condition wherein fuel changes from a normally liquid state to a gaseous state within the fuel ring or injector body, obstructing the flow of liquid fuel and adversely affecting fuel metering and engine performance.
Dual-coil fuel injectors are known to reduce heat generation. However, dual-coil injectors require three connections to the Engine Control Unit (ECU), a common center tap and two control connections, in contrast, only two connections to the ECU are required for single-coil injectors. The dual-coil third connection results in increased cost and complexity owing to the need to precisely align the electrical leads from the coils through sealing o-rings to connector terminals during the assembly process. In addition, the dual-coil third connection necessitates additional wire and connector hardware in the injector harness, resulting in increased cost and complexity over single-coil designs.
Single-coil fuel injectors solve many of the manufacturing and hardware cost problems described above. However, prior single-coil injector driver circuits have been known to dissipate excessive energy in the form of heat within the injector coil, making them unsuitable for LPG applications due to the risk of vapor lock. Thus, a need exists for a highly efficient, self-triggered monostable single-coil fuel injector driver circuit suitable for use with LPG systems that delivers the performance normally associated with peak and hold drivers while actually being interfaced to an ECU that only provides a saturated transistor driver. Further, a need exists for a single-coil fuel injector driver circuit capable of being mounted within a single-coil LPG injector housing without causing excessive heat build up within the injector.
The present invention provides a fuel metering device actuated by an electromagnetic assembly. The electromagnetic assembly includes a coil and armature. A housing cinctures the fuel metering device. An electrical connector is disposed on the housing, the electrical connector includes two pins that are exposed to the exterior of the fuel injector. A self-triggering driver circuit is disposed within the housing. The driver circuit has two inputs, each operatively connected to one of the connector pins. The driver circuit is configured to generate a predetermined current profile in the coil upon an initiation signal. The initiation signal is created by generating an electrical potential between the connector pins. In a preferred embodiment, the fuel injector housing includes an over-molded member. In a preferred embodiment, the fuel injector is a liquid propane fuel injector.
In a preferred embodiment, the self-triggering driver circuit has a current source that generates a current in a electromechanical valve coil. A current sensor senses the current flowing through the coil. A current threshold generator, having a peak current threshold state, corresponding to a peak current value generated by the current source, and a hold current threshold state, corresponding to a hold current value generated by the current source, transitions from the peak current threshold state to the hold current threshold state when the current sensor senses a predetermined peak current flowing through the coil. A current regulator regulates the output of the current source according to the state of the current threshold generator. A rapid decay generator is activated upon transition of the current threshold generator from the peak current threshold state to the hold current threshold state. The rapid decay generator causes rapid current decay through the coil from the peak current value to the hold current value, thus minimizing the energy dissipated in the form of heat within the coil.